1. Field of Invention
The invention relates to a micro-electromechanical device and in particular, to a micro-electromechanical device having a micro suspended structure. The invention also relates a manufacturing method thereof.
2. Related Art
The current semiconductor manufacturing technology has been well developed. With the enhancement of the technology, the complementary metal-oxide semiconductor (CMOS) manufacturing technology for manufacturing a micro-electromechanical device has become one of the frequently used technologies in the industry.
In the micro-electromechanical device, a suspended metal structure usually serves as a sensing or driving unit, which receives a driving signal (e.g., voltage or current) and then generates a magnetic force to actuate the suspended metal structure to perform the sensing or driving operation.
As shown in FIG. 1A, a conventional micro-electromechanical device 10 includes a substrate 11, and a plurality of dielectric layers 12 and a plurality of patterned metal layers 13 alternately stacked on the substrate 11. Then, as shown in FIG. 1B, portions of the dielectric layers 12 are removed by isotropic etching so that the micro-electromechanical device 10 shown in FIG. 1C is formed. However, because the portions of the dielectric layers 12 are removed by the isotropic etching, the etching time has to be precisely controlled to prevent the problem that the patterned metal layers 13 cannot be suspended due to the insufficient etching time, or that too large portions of the dielectric layers 12 are removed to reduce the structure intensity of a fixed end 17 due to the over etching time. In addition, in the CMOS manufacturing process, a thickness of each patterned metal layers is usually only several thousands of angstroms (Å) so that the rigidity of the patterned metal layer is insufficient and the micro-electromechanical device 10 may be deformed.
As shown in FIG. 2A, another conventional micro-electromechanical device 20 includes a plurality of insulating layers 24 and a plurality of patterned metal layers 23 alternately stacked on a substrate 21. Next, as shown in FIG. 2B, portions of the insulating layers 24 are removed by anisotropic etching. Then, as shown in FIG. 2C, a portion of the substrate 21 is removed by isotropic etching so that the structure constituted by the patterned metal layers 23 and portions of the insulating layers 24 can be suspended. Although this arrangement can increase the rigidity of the micro-electromechanical device 20, only the single-layer suspended structure can be manufactured. That is, the flexibility in design is insufficient. In addition, the etching time still has to be precisely controlled in order to prevent the over-etching or under-etching phenomenon.
In addition, as shown in FIG. 3A, another micro-electromechanical device 30 includes a substrate 31 having a conductive portion 35 and a sacrificial layer 36. A plurality of insulating layers 34 and patterned metal layers 33 are alternately formed on the substrate 31. As shown in FIG. 3B, portions of the insulating layers 34 are removed by anisotropic etching, and then a portion of the sacrificial layer 36 is removed by isotropic etching. Therefore, as shown in FIG. 3C, the micro-electromechanical device 30 is formed. However, the sacrificial layer 36 has a limited thickness (about several thousands of angstroms), so the micro-electromechanical device 30, which is constituted by the insulating layers 34 and the patterned metal layers 33, may stick on the conductive portion 35 of the substrate 31, thereby causing the malfunction.
Therefore, it is an important subject to provide a micro-electromechanical device and a manufacturing method thereof, in which the structure intensity can be enhanced and the manufacturing processes can be simplified.